1. Field of the Invention
The present invention relates to an automatic document feeder mounted on an image processor such as a copying machine, a facsimile, or an image reader and so adapted as to feed an original from which an image is to be read by the image processor to a reading section of the image processor and return the original from which the image has been read to a tray and an original platen.
2. Description of Related Art
An automatic document feeder mounted on a copying machine, for example, and so adapted as to automatically feed an original set on an original platen to a transparent platen of the copying machine and then return the original to a tray and the original platen has been conventionally known.
In this type of the automatic document feeder, the originals set on the original platen are fed to a conveying path by feeding means such as a feeding belt. The originals (a bundle of originals) fed are separated one at a time by separating means arranged in the conveying path, and only the lowermost original is further fed to the conveying path on the downstream side of the separating means.
The original thus fed is stopped for a predetermined time period in a state where its leading end abutted against a nip portion of a pair of registration rollers, thereby preventing so-called diagonal original feeding.
Thereafter, the rotation of the registration rollers is started at the same timing as operations in the main body of the copying machine. Consequently, the conveyance of the original is resumed, so that the original is led onto the transparent platen. Therefore, an image formed on one surface of the original is read.
On the other hand, in a copying machine capable of making duplex copies of an original, an image formed on one surface of the original is read on a transparent platen. Thereafter, the original is conveyed by a reversing roller along a reversing path for bypassing a part of a conveying path in the opposite direction, and is arranged on the transparent platen again, so that an image formed on the other surface of the original is read.
In order to miniaturize a conveying mechanism, it is considered that one of the pair of registration rollers arranged with the conveying path interposed therebetween is also used for the reversing roller.
In such a case, however, the following new problem arises. Specifically, in a case where the pair of registration rollers performs the function of only a registration, both the registration rollers are composed of polyacetal resin (POM) which easily slides. On the other hand, when one of the registration rollers is also used for the reversing roller, the one registration roller is made of rubber, and the other registration roller is made of POM. Therefore, the leading end of the original does not easily enter a contact portion (also referred to as a nip portion) of the registration rollers, so that the original may be jammed and damaged.